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CAPC Releases 2021 Parasite Forecast

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2021 Parasite Forecast says Heartworm to be above average, with Lyme disease expanding south and west.

The Companion Animal Parasite Council (CAPC) – the nation’s leading source on parasitic diseases that threaten the health of pets and people – released its annual 2021 Parasite Forecast and corresponding 30-day Pet Parasite Forecast maps to alert pet owners of impending outbreaks across the United States. CAPC predicts heartworm transmitted by mosquitoes will be higher than average, especially along the Atlantic coast and Mississippi river, with increased risk in parts of California, Idaho, and Montana. The risk for Lyme disease, transmitted by ticks, continues to expand southward and westward with “hot spots” expected in portions of Michigan and Ohio, heightened risk persisting in the Northeast, and movement into the southern states, including the Carolinas and Tennessee.

“Because of the dynamic and ever-changing nature of parasites, we started providing our annual forecasts more than nine years ago,” said Dr. Christopher Carpenter, DVM, and chief executive officer of CAPC. “Over the years, we’ve seen the risk for parasitic diseases continue to increase and expand into areas that have had historically lower prevalence. CAPC’s 2021 Parasite Forecast is critical to alerting pet owners to the risks this year and reinforcing CAPC’s recommendation that all pets need to be annually tested and protected year-round.”


Pet owners and veterinarians who want to monitor parasitic disease risk in their county throughout the year now have access to 30-Day Pet Parasite Forecast Maps at petdiseasealerts.org. These maps, developed exclusively by CAPC, provide a local forecast for every county in the continental United States and are updated monthly. This free service informs pet owners about the continuous risk in their local communities and reminds them about the importance of annual parasite testing and year-round parasite protection.

According to CAPC, the risk of acquiring heartworm disease in 2021 is very real due to the expansive nature of the disease. Mosquitoes are responsible for transmitting the parasite that causes heartworm disease, which can be deadly to pets. This increase in heartworm prevalence can be attributed to several factors, including warmer and humid weather patterns that create ideal breeding conditions for mosquitoes; transportation of companion animals from one area of the country to another; and pet owners who don’t administer parasite preventatives 12 months of the year.

Heartworm isn’t the only threat pet owners will need to be watchful for. CAPC also predicts that Lyme disease, a potentially fatal disease for pets, is expanding quickly. Transmitted by ticks, Lyme disease is spreading due to the expansion of tick host habitat range, primarily deer and rodents, and migratory birds carrying ticks to new areas. Warmer weather and longer seasons for tick reproduction is also a factor. Veterinarians and pet owners should test pets annually and use tick preventatives year-round. Pets in high-risk areas should be tested and consider a vaccination for Lyme disease.

Photo of mosquito representative of pet parasite report.

Risk areas

The forecasts support CAPC’s recommendation for annual testing and having pets on preventive treatment year-round. For 2021, CAPC predicts the following risk areas for parasite-related diseases:

  • Infection with heartworm, which causes a potentially fatal disease, is expected to be higher than average along the Mississippi River, throughout southern portions of the Midwest, and along the Atlantic Coast north into Virginia and southern New Jersey. Increased risk is also expected in southern Arizona, New Mexico, and portions of Colorado, Kansas, Montana, and North Dakota. Unique to this year’s forecast is increased risk in northern California, Idaho, and western Montana. In addition, states with historically lower prevalence of heartworm are at increasing risk, including central and southern Florida, Indiana, central and northern Illinois, southern Iowa, as well as lower Michigan and Ohio in the Great Lakes region. Much of the upper Midwest and New England region is expected to have little change, but small increases in prevalence may be seen throughout. Pet owners should take extra care to limit their pets’ exposure to mosquitoes, test their pets annually for heartworm disease, and use heartworm preventatives year-round.
  • Lyme disease is a high threat and continues to expand southward and westward. There is a higher-than-average seroprevalence predicted throughout eastern Kentucky, northeastern Tennessee, western Michigan, and Ohio, with high-risk “hot spots” expected in northwestern and southwestern Michigan and southern and northeastern Ohio. High risk persists throughout the Northeast, including Wisconsin, Minnesota, and the upper peninsula of Michigan. A higher-than-normal risk is expected in North Dakota, northern South Dakota, Iowa, southern Illinois, and western Kentucky. The southward movement of Lyme is evident in the increasing risk in the Carolinas and Tennessee. Pets living in or traveling to these states are considered at high risk. Pet owners should talk to their veterinarian about a Lyme vaccination in addition to testing for the disease and protecting pets year-round against ticks.
  • Ehrlichiosis, transmitted by ticks, is expected to be above normal for the majority of the United States, particularly in New Mexico, Arizona, southern California, northern Colorado, and southern Wyoming, as well as central and northeastern Illinois and parts of Wisconsin and Minnesota. Risk is expected to remain high throughout the southwest, south-central, and coastal Atlantic states. CAPC recommends protecting pets year-round against ticks and routine examination of pets for the presence of ticks. Prompt removal of ticks is imperative.
  • Anaplasmosis, also transmitted by ticks, is expected to have increased risk, including areas where pets have historically had low exposure to the disease. Increased risks are expected to the north and east of its traditional New England prevalence, as well as in western regions of Pennsylvania and New York. Risk remains high in Wisconsin, Minnesota, and eastern North Dakota. Higher than average increases are expected in portions of Virginia, West Virginia, west and south Texas, and northern California. These areas and surrounding regions have historically had a lower risk of exposure. In light of these predicted changes, pet owners should be vigilant in protecting pets with year-round tick preventatives and annual testing. Pet owners are encouraged to regularly check their pets for ticks and remove them promptly.

For more information about the Companion Animal Parasite Council visit capcvet.org. To view local 30-Day Pet Parasite Forecast Maps, visit petdiseasealerts.org.

Parasite Forecast Map

How the forecasts are created

The annual CAPC Pet Parasite Forecasts are a collaborative effort from parasitologists and statisticians in leading academic institutions across the United States who engage in ongoing research and data interpretation to better understand and monitor vector-borne disease agent transmission and changing life cycles of parasites. The forecasts are based on many factors, including temperature, precipitation, and population density.

About the Companion Animal Parasite Council

The Companion Animal Parasite Council (capcvet.org) is an independent not-for-profit foundation comprised of parasitologists, veterinarians, medical, public health, and other professionals that provides information for the optimal control of internal and external parasites that threaten the health of pets and people. Formed in 2002, CAPC works to help veterinary professionals and pet owners develop the best practices in parasite management that protect pets from parasitic infections and reduce the risk of zoonotic parasite transmission.